qeth: restore device features after recovery

After device recovery, only a basic set of network device features is
enabled on the device. If features like checksum offloading or TSO were
enabled by the user before the recovery, this results in a mismatch
between the network device features, that the kernel assumes to be
enabled on the device, and the features actually enabled on the device.

This patch tries to restore previously set features, that require
changes on the device, after the recovery of a device. In case of an
error, the network device's features are changed to contain only the
features that are actually turned on.

Signed-off-by: Hans Wippel <hwippel@linux.vnet.ibm.com>
Signed-off-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>